Catalytic reforming is a well established petroleum process for improving the octane quality of naphthas and straight run gasolines. In fact, it is the primary source of octane in the modern refinery. Reforming can be defined as the total effect of the molecular changes, or hydrocarbon reactions, produced by dehydrogenation of cyclohexanes and dehydroisomerization of alkylcyclopentanes to yield aromatics; isomerization of n-paraffins; isomerization of alkylcycloparaffins to yield cyclohexanes; isomerization of substituted aromatics; and hydrocracking of paraffins which produces gas, and inevitably coke, the latter being deposited on the catalyst. In catalytic reforming, a multifunctional catalyst is usually employed, which contains a hydrogenation-dehydrogenation component, or components, usually platinum, substantially atomically dispersed on the surface of a porous, inorganic oxide supporter. While such catalysts are widely used in the industry today, they are limited in their use to relatively high pressures and temperatures, which are needed to obtain desirable liquid yields. Thus, much work is being done to develop catalyst systems which will operate at lower temperatures and pressures without substantial loss in activity. One such catalyst system which has been suggested includes the use of noble metal large pore zeolites which might provide greater dehydrocyclization selectivity and hence better liquid yields when compared to conventional reforming catalysts.
The leading candidates among the zeolites for use in catalytic reforming are faujasites and L-type zeolites. Faujasites, with their large, three dimensional, pore system continue to play a dominant role in the petroleum industry as excellent hydrocarbon conversion catalysts. While much work has been done through the years in developing faujasites for petroleum industry use, it has primarily been directed to their use in fluid catalytic cracking (FCC). This of course being the case since FCC plays such an important role in the modern refinery for producing gasoline by the most economical route.
Because of the availability of large quantities of such large pore zeolites, attempts have been made to use them as supports for reduced metals to catalyze hydrogenation-dehydrogenation reactions, which reactions are important in catalytic reforming. The primary petroleum applications, other than FCC, in which some degree of commercial success has been achieved using large pore zeolites has been at relatively high hydrogen pressures over nickel on offeritite and palladium on ultra stable Y zeolite for selective hydrocracking.
Attempts have been made to incorporate noble metals onto the alkaline faujasites sodium zeolite X, and sodium zeolite Y, as well as on zeolite L, for use in such lower pressure processes as aromatization, hydrogenation, and isomerization, all of which are important reactions for catalytic reforming. For example, U.S. Pat. No. 4,417,083, teaches the incorporation of noble metals onto zeolites such as faujasites X, faujasite Y, and zeolite L by: impregnation with an aqueous solution of a salt, or of a platinum complex such as hexachloroplatinic acid, dinitrodiaminoplatinum or platinum tetramine chloride; and by ion exchange with an aqueous solution of a platinum cationic complex like platinum tetramine chloride. Ion-exchange is also taught in U.S. Pat. No. 3,953,365. While such noble metal zeolite catalysts show improvement over conventional noble metal alumina catalysts, with regard to dehydrocyclization, they suffer from the disadvantage of coking at pressures most desirable for reforming. Furthermore, because of their limited pore size, L-type zeolites face an additional problem in that their pores become blocked when faced with full range naphthas which contain hydrocarbons having eight or more carbon atoms.
Recently, platinum in zeolite L has been proposed as a catalyst for paraffin aromatization at relatively mild conditions. However, platinum in the faujasite structure, when prepared in substantially the same way as the preparation of platinum in zeolite L, does not give acceptable hydroconversion catalytic activity, selectivity, and stability.
Consequently, there still exits a need in the art for the development of large pore zeolites in such petroleum processes as reforming, isomerization, and hydrogenation. There is a particular need for a large pore zeolite, such as a faujasite, that will not coke excessively at relatively low pressure hydroconversion conditions, that can be pushed to relatively high temperatures to achieve additional conversion, and that will be able to withstand petroleum feedstocks having relatively heavy hydrocarbons.